An organic electronic device means a device that needs charge exchanges between an electrode and an organic material using holes and/or electrons. An organic electronic device can be categorized into two main groups depending on operation principles. First is an electric device in which excitons form in an organic material layer by the photons brought into the device from an external light source, these excitons are separated into electrons and holes, and these electrons and holes are used as a current source (voltage source) by each of these being transferred to different electrodes. Second is an electronic device in which holes and/or electrons are injected to an organic material semiconductor that forms an interface with an electrode by applying voltage or current to two or more electrodes, and the device is operated by the injected electrons and holes.
Examples of an organic electronic device include an organic light emitting device, an organic solar cell, an organic transistor, and the like, and these all need a hole injection or transfer material, an electron injection or transfer material, or a light emitting material for the driving of the device. Hereinafter, an organic solar cell will be described in detail mostly, however, in the organic electronic devices described above, the hole injection or transfer material, the electron injection or transfer material, or the light emitting material is used under similar principles.
The possibility of an organic solar cell was first presented in 1970s, but the organic solar cell had no practical use since the efficiency was too low.
However, since C. W. Tang of Eastman Kodak showed the possibility of commercialization as various solar cells with a double layer structure using copper phthalocyanine (CuPc) and perylene tetracarboxylic acid derivatives in 1986, interests in organic solar cells and related researches have rapidly increased bringing in a lot of progresses.
Since then, organic solar cells have made innovative progresses in terms of efficiency as the concept of a bulk heterojunction (BHJ) was introduced by Yu et al. in 1995, and fullerene derivatives of which solubility is improved such as PCBM have been developed as an n-type semiconductor material.
However, problems such that fullerene, a starting material, is expensive, difficult to synthesize and does not have favorable solubility, are still blocking the development of electron acceptor materials. The development of electron donor materials having a low band gap and new electron acceptor materials having favorable charge mobility has been continuously attempted in order to replace existing materials.